Numerous animal studies and human clinical trials have demonstrated the potential of cytokines as cancer immunotherapeutics. However, due to heterogeneity of human cancers, each cytokine is likely to cure only limited types of cancers. A novel cytokine, IFN-gamma-inducing factor (IGIF), has recently been cloned and shown to strongly induce IFN- gamma production, stimulate T cell proliferation and augment NK cell activity in vitro. The immunological characteristics of IGIF are strikingly reminiscent of IL-12, the most potent antitumor cytokine identified yet. Since the antitumor effects of IL-12 are largely dependent on IFN-gamma induction, and since IGIF induces more IFN- gamma than IL-12, it is possible that IGIF is also a potent antitumor agent, either on its own or in combination with other cytokines. We have recently demonstrated that IGIF induces IFN-gamma production in vivo, up-regulates MHC class I expression in Renca tumor cells in vitro, and elicits long-term antitumor immunity against Renca and K1735 tumors in vivo. In this application, we propose to explore the potential of IGIF as a cancer immunotherapeutic. In Specific Aim 1, we will generate reagents including IGIF antisera, IGIF-high expression vectors and tumor cell transfectants, which are necessary for the IGIF studies proposed here. To determine the mechanisms through which IGIF exerts its antitumor effects, Specific Aim 2 will evaluate in the established Renca tumor model, the IGIF antitumor efficacies by using different approaches, including IGIF-transduced Renca cells, recombinant IGIF protein as well as in vivo skin transfection of IGIF cDNA by a gene gun. Once Renca tumor regression by IGIF is demonstrated, tumor-infiltrating immune cells will be characterized, and the effector cells determined. Specific Aim 3 will examine the role of endogenous IGIF in tumor rejection as well as explore the functional relationship between IGIF and IL-2 using the spontaneous rejecting tumor models. Finally, to evaluate the potential of IGIF as a potent, curative antitumor therapeutic, Specific Aim 4 will examine IGIF antitumor effects in several tumor models that are less responsive to IL-12 immunotherapy. Specific Aim 4 will also determine potential synergism between IGIF and other immunomodulatory molecules, including IL-2, B7.1 and IL-12, in adjunctive antitumor therapies. New knowledge gained from these studies may eventually increase the spectrum of human cancers curable by immunotherapeutics.